This application for the K23 award will provide Dr. Sarah Taylor with five-years protected time and funding to: (1) both define vitamin D sufficiency in preterm infants and identify the vitamin D requirements to achieve and maintain sufficiency and (2) to develop her career in clinical research with training in biostatistics and epidemiology as well as the ethics of clinical research. With improved understanding of optimal vitamin D status and the known serious health consequences of vitamin D deficiency, Dr. Taylor's research plan will be at the forefront of research that addresses the national public health concern of vitamin D deficiency. Premature infants are at great risk of vitamin D deficiency due to the high prevalence of maternal deficiency during gestation, limited exposure to UV light, and problematic nutritional and vitamin support. Dr. Taylor has developed the first study to evaluate vitamin D status in the very low birth weight infant population as related to biomarkers of calcium homeostasis, bone health, parathyroid function, and immune-response cytokines. After identifying the vitamin D status that denotes sufficiency, Dr. Taylor will perform an interventional trial of vitamin D supplementation to assess the vitamin D intake required to achieve and maintain sufficiency and avoid complications of vitamin D deficiency in all preterm infants. Dr. Taylor is initiating this project with the support and guidance of her co-mentors who are well-established in the investigation of vitamin D deficiency and its effects. She also has the support of the GCRC and the Division of Neonatology in the Department of Pediatrics. With the goal to become an independent academic clinician, Dr. Taylor will obtain a Master of Science degree in Clinical Research during the K23 award. She also will be actively involved in promoting clinical research ethics educational opportunities at MUSC through coordination of a weekly seminar series and work group involvement. As Dr. Taylor completes her research study and her training in clinical research afforded by this award, she will expand upon the study results to further investigate nutritional needs of infants as an independent clinical researcher.